Dealing with Rats

[Geritt Shipley]

Hello, I've got a single family home in Portland, OR and the tenants began hearing rats in the attic about a month ago. Since then I have located the area where they entered and sealed it off, however I'm having trouble killing the ones currently living in the attic. Has anyone had success with Rat poison and if so which one? I've been using Rat X and am convinced it doesn't actually kill them, currently just have snap traps in place. Any advice on the matter is greatly appreciated.